[Rostok]

did you declare your Postupdate function before the declaration of your hb ?

lib.PostUpdateHealth = function(Health, min, max)
    local d = floor(min/max*100)
    Health.Filling:SetHeight((min / max) * Health:GetWidth())
    Health.Filling:SetTexCoord(0,1,  math.abs(min / max - 1),1)
end